Firstly, recent developments in the study of choice behavior were reviewed. Secondly, choice in auditory attention (allocation of attention) in a vigilance task was examined and the results suggested that human subjects showed deviation from rational choice (matching law) in such a vigilance situation. thirdly, effects of relative density and probability of reinforcement on human self-control were investigated. Forty-eight adult humans were divided into four groups and given a choice between an immediate small reward and a delayed large reward. Each subject experienced three combinations of rewards differing in the relative density of reinforcement (the number of points divided by the time between reinforcements). Reinforcement probability was manipulated across the groups. When the probability was 1.0, subjects always chose rewards with larger densities. When the probability was less than 1.0, however, choice proportions for the rewards with larger densities decreased as the probability decreased, suggesting that relative density does not accurately describe human choice under such conditions. Fourthly, in order to examine factors affecting deviation from rational choice, rates of temporal discounting were examined with Japanese young and elder participants. In addition, rates of discounting from young adults living alone and those living with their families were compared in order to examine effects of money-management experience on temporal discounting. The results suggests that this methodology might be useful in examining factors affecting deviation from rational choices in humans.